设定a为N(0,1)的500个随机数和量化级数n＝64， 调用u_pcm.m, 分别输出sqnr、a(1:5)、a_quan(1:5)、code(1:5,:)。 -Set a for the N (0,1) of 500 random numbers and quantify the series n = 64, call u_pcm.m, respectively output sqnr, a (1:5), a_quan (1:5), code (1 : 5,:).